New CONST_VECTOR layout

This patch makes CONST_VECTOR use the same encoding as VECTOR_CST.

One problem that occurs in RTL but not at the tree level is that a fair
amount of code uses XVEC and XVECEXP directly on CONST_VECTORs (which is
valid, just with looser checking).  This is complicated by the fact that
vectors are also represented as PARALLELs in some target interfaces,
so using XVECEXP is a good polymorphic way of handling both forms.

Rather than try to untangle all that, the best approach seemed to be to
continue to encode every element in a fixed-length vector.  That way only
target-independent and AArch64 code need to be precise about using
CONST_VECTOR_ELT over XVECEXP.

After this change is no longer valid to modify CONST_VECTORs in-place.
This needed some fix-up in the powerpc backends.

2018-01-02  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	* doc/rtl.texi (const_vector): Describe new encoding scheme.
	* Makefile.in (OBJS): Add rtx-vector-builder.o.
	* rtx-vector-builder.h: New file.
	* rtx-vector-builder.c: Likewise.
	* rtl.h (rtx_def::u2): Add a const_vector field.
	(CONST_VECTOR_NPATTERNS): New macro.
	(CONST_VECTOR_NELTS_PER_PATTERN): Likewise.
	(CONST_VECTOR_DUPLICATE_P): Likewise.
	(CONST_VECTOR_STEPPED_P): Likewise.
	(CONST_VECTOR_ENCODED_ELT): Likewise.
	(const_vec_duplicate_p): Check for a duplicated vector encoding.
	(unwrap_const_vec_duplicate): Likewise.
	(const_vec_series_p): Check for a non-duplicated vector encoding.
	Say that the function only returns true for integer vectors.
	* emit-rtl.c: Include rtx-vector-builder.h.
	(gen_const_vec_duplicate_1): Delete.
	(gen_const_vector): Call gen_const_vec_duplicate instead of
	gen_const_vec_duplicate_1.
	(const_vec_series_p_1): Operate directly on the CONST_VECTOR encoding.
	(gen_const_vec_duplicate): Use rtx_vector_builder.
	(gen_const_vec_series): Likewise.
	(gen_rtx_CONST_VECTOR): Likewise.
	* config/powerpcspe/powerpcspe.c: Include rtx-vector-builder.h.
	(swap_const_vector_halves): Take an rtx pointer rather than rtx.
	Build a new vector rather than modifying a CONST_VECTOR in-place.
	(handle_special_swappables): Update call accordingly.
	* config/rs6000/rs6000-p8swap.c: Include rtx-vector-builder.h.
	(swap_const_vector_halves): Take an rtx pointer rather than rtx.
	Build a new vector rather than modifying a CONST_VECTOR in-place.
	(handle_special_swappables): Update call accordingly.

From-SVN: r256102

2 files changed, 28 insertions, 26 deletions

diff --git a/gcc/config/powerpcspe/powerpcspe.c b/gcc/config/powerpcspe/powerpcspe.c
index 520f2e1..f5868dd 100644
--- a/gcc/config/powerpcspe/powerpcspe.c
+++ b/gcc/config/powerpcspe/powerpcspe.c
@@ -79,6 +79,7 @@
 #endif
 #include "case-cfn-macros.h"
 #include "ppc-auxv.h"
+#include "rtx-vector-builder.h"
 
 /* This file should be included last.  */
 #include "target-def.h"
@@ -42581,23 +42582,24 @@ mark_swaps_for_removal (swap_web_entry *insn_entry, unsigned int i)
     }
 }
 
-/* OP is either a CONST_VECTOR or an expression containing one.
+/* *OP_PTR is either a CONST_VECTOR or an expression containing one.
    Swap the first half of the vector with the second in the first
    case.  Recurse to find it in the second.  */
 static void
-swap_const_vector_halves (rtx op)
+swap_const_vector_halves (rtx *op_ptr)
 {
   int i;
+  rtx op = *op_ptr;
   enum rtx_code code = GET_CODE (op);
   if (GET_CODE (op) == CONST_VECTOR)
     {
-      int half_units = GET_MODE_NUNITS (GET_MODE (op)) / 2;
-      for (i = 0; i < half_units; ++i)
-	{
-	  rtx temp = CONST_VECTOR_ELT (op, i);
-	  CONST_VECTOR_ELT (op, i) = CONST_VECTOR_ELT (op, i + half_units);
-	  CONST_VECTOR_ELT (op, i + half_units) = temp;
-	}
+      int units = GET_MODE_NUNITS (GET_MODE (op));
+      rtx_vector_builder builder (GET_MODE (op), units, 1);
+      for (i = 0; i < units / 2; ++i)
+	builder.quick_push (CONST_VECTOR_ELT (op, i + units / 2));
+      for (i = 0; i < units / 2; ++i)
+	builder.quick_push (CONST_VECTOR_ELT (op, i));
+      *op_ptr = builder.build ();
     }
   else
     {
@@ -42605,10 +42607,10 @@ swap_const_vector_halves (rtx op)
       const char *fmt = GET_RTX_FORMAT (code);
       for (i = 0; i < GET_RTX_LENGTH (code); ++i)
 	if (fmt[i] == 'e' || fmt[i] == 'u')
-	  swap_const_vector_halves (XEXP (op, i));
+	  swap_const_vector_halves (&XEXP (op, i));
 	else if (fmt[i] == 'E')
 	  for (j = 0; j < XVECLEN (op, i); ++j)
-	    swap_const_vector_halves (XVECEXP (op, i, j));
+	    swap_const_vector_halves (&XVECEXP (op, i, j));
     }
 }
 
@@ -42900,8 +42902,7 @@ handle_special_swappables (swap_web_entry *insn_entry, unsigned i)
       {
 	/* A CONST_VECTOR will only show up somewhere in the RHS of a SET.  */
 	gcc_assert (GET_CODE (body) == SET);
-	rtx rhs = SET_SRC (body);
-	swap_const_vector_halves (rhs);
+	swap_const_vector_halves (&SET_SRC (body));
 	if (dump_file)
 	  fprintf (dump_file, "Swapping constant halves in insn %d\n", i);
 	break;
diff --git a/gcc/config/rs6000/rs6000-p8swap.c b/gcc/config/rs6000/rs6000-p8swap.c
index 7d9ab87..e0d8f31 100644
--- a/gcc/config/rs6000/rs6000-p8swap.c
+++ b/gcc/config/rs6000/rs6000-p8swap.c
@@ -36,6 +36,7 @@
 #include "expr.h"
 #include "output.h"
 #include "tree-pass.h"
+#include "rtx-vector-builder.h"
 
 /* Analyze vector computations and remove unnecessary doubleword
    swaps (xxswapdi instructions).  This pass is performed only
@@ -931,23 +932,24 @@ mark_swaps_for_removal (swap_web_entry *insn_entry, unsigned int i)
     }
 }
 
-/* OP is either a CONST_VECTOR or an expression containing one.
+/* *OP_PTR is either a CONST_VECTOR or an expression containing one.
    Swap the first half of the vector with the second in the first
    case.  Recurse to find it in the second.  */
 static void
-swap_const_vector_halves (rtx op)
+swap_const_vector_halves (rtx *op_ptr)
 {
   int i;
+  rtx op = *op_ptr;
   enum rtx_code code = GET_CODE (op);
   if (GET_CODE (op) == CONST_VECTOR)
     {
-      int half_units = GET_MODE_NUNITS (GET_MODE (op)) / 2;
-      for (i = 0; i < half_units; ++i)
-	{
-	  rtx temp = CONST_VECTOR_ELT (op, i);
-	  CONST_VECTOR_ELT (op, i) = CONST_VECTOR_ELT (op, i + half_units);
-	  CONST_VECTOR_ELT (op, i + half_units) = temp;
-	}
+      int units = GET_MODE_NUNITS (GET_MODE (op));
+      rtx_vector_builder builder (GET_MODE (op), units, 1);
+      for (i = 0; i < units / 2; ++i)
+	builder.quick_push (CONST_VECTOR_ELT (op, i + units / 2));
+      for (i = 0; i < units / 2; ++i)
+	builder.quick_push (CONST_VECTOR_ELT (op, i));
+      *op_ptr = builder.build ();
     }
   else
     {
@@ -955,10 +957,10 @@ swap_const_vector_halves (rtx op)
       const char *fmt = GET_RTX_FORMAT (code);
       for (i = 0; i < GET_RTX_LENGTH (code); ++i)
 	if (fmt[i] == 'e' || fmt[i] == 'u')
-	  swap_const_vector_halves (XEXP (op, i));
+	  swap_const_vector_halves (&XEXP (op, i));
 	else if (fmt[i] == 'E')
 	  for (j = 0; j < XVECLEN (op, i); ++j)
-	    swap_const_vector_halves (XVECEXP (op, i, j));
+	    swap_const_vector_halves (&XVECEXP (op, i, j));
     }
 }
 
@@ -1251,8 +1253,7 @@ handle_special_swappables (swap_web_entry *insn_entry, unsigned i)
       {
 	/* A CONST_VECTOR will only show up somewhere in the RHS of a SET.  */
 	gcc_assert (GET_CODE (body) == SET);
-	rtx rhs = SET_SRC (body);
-	swap_const_vector_halves (rhs);
+	swap_const_vector_halves (&SET_SRC (body));
 	if (dump_file)
 	  fprintf (dump_file, "Swapping constant halves in insn %d\n", i);
 	break;